Individual simulcast station control system

ABSTRACT

A simulcast paging transmitter remote control system capable of individual station control is described. The remote paging transmitter control system comprises an encoder and decoder which interface with a paging terminal and transmitter respectively. The system encoder and decoder communicate through a specifically formatted signalling scheme which is configured to provide station deactivation information as well as conventional paging information.

BACKGROUND OF THE INVENTION

This invention relates to the field of paging simulcast transmissionsystems and specifically to a simulcast transmission system in whicheach individual simulcast transmitter in the system can be individuallyactivated or "knocked down" in response to a signal from a pagingterminal or central controller.

In the past simulcast transmission systems have incorporatedtransmitting stations which remained activated while the simulcastsystem was in use. Individual remote station control systems have notbeen developed with efficient signalling schemes.

Wide area coverage systems employing multiple transmitters on the sameRF channel are gaining wider acceptance due in part to the growth ofpersonal paging activity. Simulcast transmission systems require thateach transmitter in the system produce a signal of substantiallyidentical frequency and modulation. This requires that the transmittingstations in a simulcast system be periodically adjusted so that criticalsystem parameters are satisfied. One method of calibrating a simulcasttransmission system is to selectively deactivate certain transmitters inthe system while active transmitters are adjusted. In a typical priorart simulcast transmission system, service personnel would be stationedat each individual transmitter location, and would communicate through aseparate telephone line or RF channel while manually activating anddeactivating remote simulcast transmitters to effect the calibrationprocedure. Prior art simulcast systems have not included any means forindividually, efficiently and remotely controlling simulcasttransmitters through a conventional simulcast system link.

In addition, individual simulcast transmitter control is useful in asimulcast system which is designed to generate multiple signallingschemes. A simulcast transmitter which can generate both binary andanalog signalling formats, can be configured for individual stationcontrol and provide a truly universal paging system with controllablearea coverage. For instance, simulcast system would typically beconfigured to provide wide area coverage in a certain area. However,paging subscriber may desire service in only a portion of the totalavailable area, for instance at a large construction site in a certainsector of a city. A simulcast transmission system with individualstation control can provide service to the limited area subscriberwithout requiring the subscriber to pay a fee based on broad areacoverage. In other words, another benefit of individual station controlis the ability to sector paging coverage based on different tariffstructures.

SUMMARY OF THE INVENTION

Briefly described, the present invention contemplates a paging remotecontrol system which comprises an encoder and decoder which interfacewith a paging terminal and transmitter, respectively. The system encodergenerates a series of tones and timed pauses in response to signalsgenerated by a paging terminal and by a series of programmable switcheslocated within the system encoder. The programmable switches within thesystem provide sector information utilized in generating the signallingscheme.

The paging system encoder then generates signals in accordance with thesignalling scheme. The signals are formatted to instruct specific pagingstations within the paging simulcast system to transmit or not transmitas instructed by the paging system encoder.

According to the signalling scheme of the present invention, the pagingsystem encoder will generate a high level guard tone signal whichinstructs the remote simulcast transmitters that paging signal isimminent. The paging system encoder then generates a group of up to 10function tones to instruct individual simulcast transmitter station thatthey should not transmit the subsequent paging signal. The function tonesequence is terminated by the transmission of a keying sequence tone.

The signalling scheme is formatted to be capable of addressing a totalof thirty individual simulcast transmitter sites through repeated use ofthe function tone sequence. Addressing more than ten simulcasttransmitters requires that each function tone sequence be delineated bya unique keying sequence tone. Any number of stations up to 30 can beaddressed by sending the sequence of high level guard tones followed byfunction tones delineated keying sequence tones.

Each of the remote paging transmitter sites is equipped with a pagingsystem decoder which has been programmed by user accessible switches torespond to a unique function and keying sequence tone, by selectivelyactuating or deactuating the paging transmitter. Every paging systemdecoder will actuate the paging transmitter if its function tone/grouptone signal has not been received and the end of sequence tone isreceived.

It is, therefore, an object of this invention to provide a pagingsimulcast remote control system and apparatus capable of selectivelydeactivating any simulcast remote transmitter used in the simulcastsystem.

It is a further object of the present invention to provide a collapsingsignalling scheme where only the specific transmitter disable tones aretransmitted.

It is yet another object of the present invention to provide a pagingsimulcast remote control system which can be interlaced withconventional paging information thereby eliminating the need foradditional control lines.

It is still another object of the present invention to provide a pagingsimulcast remote control system which can be programmed to providevariable sector coverage.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a paging of the type which embody thesignalling scheme of the present invention.

FIGS. 2a-h show the signalling scheme which unifies the operation of theencoder and decoder of the present invention.

FIGS. 3a and 3b is an electrical schematic of the encoder whichgenerates the required signalling scheme of the present invention.

FIGS. 4 through 14 are flow diagrams which define the operation of themicrocomputer used in the encoder of FIG. 3.

FIG. 15 is an electrical schematic of the decoder which decodes therequired signalling scheme of the present invention.

FIG. 16 is a detailed electrical schematic of the function tone decoderof the individual station controller of FIG. 3.

FIG. 17 through 28b are flow diagrams which define the operation of themicrocomputer used in the encoder of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a block diagram of a paging system of the type whichembodies the signalling scheme utilized in the present invention. Theillustrated paging system includes a paging terminal (10) adapted toprovide analog or binary paging signals. The paging terminal interfaceswith a modem 12 and a paging system encoder 14. The modem 12 is aconventional device which converts a binary signal from the pagingterminal 10 to a frequency-shift keying (FSK) signal used by the stationencoder 14. The paging terminal 10 cooperates with the paging systemencoder 14 by providing signals to the encoder 14 which indicate thatthe paging terminal 10 is about to transmit binary or analog signals.The encoder 14 then signals the paging terminal 10 when the encoder isready to receive either type of signalling. An exact description of thepaging terminal and the interface signals required by the paging systemencoder are described in Motorola document 68P81063E15 (1982) entitled"Simulcast System Controller and PURC Station Controller" available fromthe Service Publication Department of Motorola, Inc., 1301 EastAlgonquin Rd., Schaumburg, Ill., or from Motrorola C & E Parts, 1313East Algonquin Rd., Schaumburg, Ill.

The encoder 14 then generates a series of tones and timed pauses whichare especially formatted and communicated to a paging base station whichincludes station decoder 16. The paging decoder is described incopending patent assignee of the present invention. The decoder 16converts the formattred signals from the encoder 14 and selectivelyactivates modem 18 and transmitter 20 in predetermined timed sequencesas determined by the signals from the encoder 14. The paging transmitter20 can then be selectively switched off or turned on in response to thesignals received from the encoder 14.

The signalling scheme shown in FIG. 2 has been developed to unify thebase station control functions required in paging systems utilizing theindividual station control control feature. The signalling scheme shownin FIG. 2 shows a control tone sequence comprising a matrix of functiontones inserted between a high level guard tone and one or more keyingsequence tones. The matrix of function tones is used to disableundesired stations. The control tones which are sent are determined bysector select programming or individual station control switchesconnected to the paging system encoder.

Each simulcast transmitter station is assigned a group and disablefunction tone. The signalling scheme is designed to produce a total of10 individual function tones and three group or keying sequence tones.The simulcast transmitter decoder is designed to respond to theappropriate keying sequence and function tones. If the appropriatecombination of tones is received, the station remains disabled until thesystem is dekeyed, then any disabled simulcast control modules arereset.

The individual station control scheme is designed to be inserted into asecond signalling scheme which allows a paging simulcast transmitter tokey in an analog or binary mode. The individual station control schemebegins with the transmission of a high level guard tone signal andterminates with a keying sequence tone. The mode keying control sequencebegins with the next control tone. The exact operation of the modekeying signalling scheme is described later in this application and adetailed description is shown in pending U.S. patent application Ser.No. 487,482 entitled Paging Universal Remote Control System by StephenDunkerton et al filed Apr. 22, 1983 and assigned to the assignee of thepresent invention.

The table below shows the function tones associated with each station.Stations 1 through 10 are always associated with group 1, stations 11through 20 in group 2 and stations 21 through 30 in group 3.

    ______________________________________                                        Station Number                                                                              Disable FT Frequency                                            ______________________________________                                        1        11     21    1750       Hz                                           2        12     22    1650                                                    3        13     23    1550                                                    4        14     24    1450                                                    5        15     25    1350                                                    6        16     26    1250                                                    7        17     27    1150                                                    8        18     28    1050                                                    9        19     29    950                                                     10       20     30    750                                                     Final Keying Sequence Tone = 1950 Hz                                          Group II Enable = 1850 Hz                                                     Group III Enable = 2050 Hz                                                    ______________________________________                                    

Referring now to FIG. 2A, a typical single transmitter control sequenceis shown. According to FIG. 2A, a binary paging signal is sent by firstsending a first binary pattern of 1's and 0's at a 75 Hz rate for a 100milliseconds. This pattern is immediately followed by the binary pagingsignal. An analog signal is transmitted by sending a high levelguardtone signal immediately followed by a low level guardtone and voicesignal. To terminate the paging sequence, a turn-off code is sent oranother binary or analog paging signal could be sent. The signallingscheme of the present invention is inserted prior to the signallingscheme of FIG. 2A for stations equipped for individual station control.

FIG. 2B shows the required signalling of the present invention for asimulcast transmission system utilizing two to thirty transmitters whereit is desired that every transmitter in the system transmits thesubsequent paging signal. As mentioned earlier, each station is equippedto decode one of ten disabling function tones, as well as one of thethree keying sequence tones. Each transmitter is also equipped to decodefinal keying sequence tone one or 1950 Hz. Therefore, according to FIG.2B, the individual station control sequence is initiated by sending ahigh level guardtone signal. Since every station is to transmit, nofunction tones are sent and the high level guardtone signal isimmediately followed by the keying sequence tone which signals the endof the function tone's sequence. After a pause of 120 ms, a singletransmission control sequence could be sent.

FIG. 2C shows a tone sequence which will instruct a ten-transmittersystem to disable every transmitter, except a single transmitter. Thecontrol sequence is initiated by sending a high level guardtone signalfollowed by a series of function tones with each function codecorresponding to a transmitter station to be disabled. The function tonesequence is terminated by a keying sequence tone which is followed by apause and then a typical single transmission control sequence.

FIG. 2D shows the control sequence required for controlling as many asten simulcast transmitters when an analog paging signal is the firstpaging signal to be transmitted.

FIGS. 2A, 2B and 2C have assumed that a single transmitter controlsequence begins with a binary page. According to the paging universalremote control scheme described in the above-mentioned patent, a binarypage is initiated by a period of pause followed by a 75 Hz signal ofbinary 1's and 0's as described above. However, if an analog pagingsignal is to be the first signal transmitted after the simulcasttransmitter control sequence, the paging system encoder must follow thelast keying sequence tone with a period of high level guardtone which isimmediately followed by a low level guardtone and analog modulationsignal as shown in FIG. 2D.

FIG. 2E shows the individual station control sequence required when asmany as twenty transmitters are to be individually controlled. Accordingto FIG. 2E, the transmitter control sequence is initiated by sending aperiod of high level guardtone followed by a group of 1 to 10 functiontone signals corresponding to group one. The group one function tonesequence is then terminated by the transmission of a group two enabletone. As many as ten function tones can then be sent which areassociated with the transmitters configured in group two. The group twofunction tone sequence is then terminated by the keying sequence tonetwo which can then be followed by a pause immediately followed by asingle transmitter control sequence. If an analog paging mode wasdesired, keying sequence tone two (KT2) could then be followed by asecond high level guardtone signal, and then a low level guardtoneaccompanied by an analog modulation signal.

FIG. 2F shows the control tone sequence which would be required tocontrol as many as thirty transmitters. According to FIG. 2F, thecontrol tone sequence is initiated by the transmission of a high levelguardtone signal immediately followed by the first grouping of functiontone signals. The first group of function tone signals is thenterminated by the transmission of a first keying sequence tone KT2,which is also a group two enable tone. The next grouping of functiontone signals are then sent terminated by a second keying sequence toneKT3. The third grouping of function tone signals can then be sentterminated by a final keying sequence tone (KT1) 1950 Hz which signalsthe end of the entire keying sequence. The final keying sequence tonecan then be followed by a pause and a single transmission controlsequence whereby a period of high level guardtone and a subsequentanalog paging signal.

FIG. 2G shows the relationship between the time interval requiredbetween the last binary paging signal and the first change oftransmitter control information. According to FIG. 2G, after the lastbinary paging signal has been transmitted, the paging encoder must pausefor at least 500 ms before retransmitting a high level guard tone signalto allow the paging system decoder to begin searching for the high levelguardtone signal.

FIG. 2H shows a relationship between additional transmitter linkstations located in the distribution paths of the paging controlsequence signal. In order to expand the range of a paging simulcastsystem, occasionally link transmitters are employed. For everyadditional link transmitter employed in the paging system, an additional300 ms period of high level guardtone must be added to the pagingtransmitter control tone sequence.

FIG. 3 is an electrical schematic of an encoder which can generate therequired signalling scheme of the present invention. A more detailedelectrical schematic of the encoder circuit of the present invention isillustrated in Motorola document 68P81063E15 entitled "Simulcast SystemController and PURC Station Controller," available from the ServicePublication Department of Motorola, Inc., 1301 East Algonquin Rd.,Schaumburg, Ill., or from Motorola C & E Parts, 1313 East Algonquin Rd.,Schaumburg, Ill. In accordance with the present invention the variouspaging output terminals are provided to the respective binary, audio andvoice input terminals of the paging system encoder. The signals areinterfaced through transformers 102, 104 and 106 respectively, whichprovide impedance matching end isolation between the paging terminal andthe paging system encoder. The transformers 102, 104 and 106 are thenconnected to buffer amplifiers 108, 110 and 112 which compensate forgain losses in the binary modem tones, paging tone and voice audiosignals. The amplifiers 108 and 110 are connected to variable resistors114 and 116 which provide further compensation between the variouspaging signals. It is desirable to adjust the binary modem tone, audiopaging tones and voice audio tones so they are substantially equal inamplitude when they are connected to summing amplifier 126. Theamplifier 112 is connected to a premphasis network 122 which conditionsthe voice audio signal and provides a standard frequency shaping used totransmit paging voice audio to remote paging transmitters. Thepremphasis network is then coupled to an amplifier 128 and a variableresistor 130 to compensate for gain variations in this signal path. Theamplifier 128 also includes a notch filter to remove the guard tonefrequency. The variable resistors 114, 116 and 130 are then coupled toelectronic mute switches 118, 120 and 124. Mute switches 118, 120 and124 can be any type electronic switch adapted to pass an electricalsignal in response to an electrical control signal. The mute switches118, 120 and 124 are coupled to a peripheral interface adaptor circuit(PIA) 132A.

The outputs of mute switches 118, 120 and 124 are coupled to a summingamplifier 126 which combines the various signals in equal proportions.The summing amplifier is then coupled to an output amplifier 134 whichis coupled to a transformer 136. The amplifier 134 and transformer 136convert the output signal of summing 126 to a signal of amplitude andimpedance required by the wire-line hookup or transmitter link used tocouple the paging system encoder 14 to the paging system decoder 16.

The summing amplifier 126 also receives an input from the variableresistor 138 which is coupled to a programmable attenuater 140. Theprogrammable attenuator 140 is coupled to two control signals from theperipheral interface adaptor 132 and a tone input from the low passfilter 142. The low pass filter 142 is coupled to a microcomputer 144.The microcomputer 144 generates the various control tone sequences ofthe paging system encoder and provides signals to the programmableattenuator 140 through PIA 132 to control the amplitude of the controltones coupled to the summing amplifier 126. The microcomputer 144 andthe PIA 132 also control the operation of the mute switches in responseto several input signals in accordance with the signalling scheme of thepresent invention. The present invention utilizes a widely usedmicrocomputer integrated circuit designated MC6803 and available fromMotorola, Inc. The companion peripheral interface adapter integratedcircuit is designated MC6821 and is also available from Motorola, Inc.

The paging system encoder 14 is configured to provide direct usercontrol via several switches, 146 through 162, which are disposed on apanel which is accessable to the user of the encoder. The switches 146,148, 150, and 152 are connected to input ports of the PIA 132. Switch146 when closed will cause the paging system encoder to enable the tone,modem and voice paths to be enabled simultaneously to the outputterminal transformer for audio level set. Likewise switch 148 whenclosed will cause a series of audio test tones, generated bymicrocomputer 144 to be placed at the output terminals of the encoder.Switches 152 and 150 are included with the paging encoder circuit toallow the paging system to accommodate additional RF link transmittersto be used in a simulcast system. For example, if a paging transmittersite is located a large distance from the paging terminal site, arepeater site will be included in the system. Each repeater site willrequire a certain amount of time to allow the repeater transmitter tokey and therefore the high level guard tone must appear for an extendedtime to allow retransmission to the paging transmitter site. Each linksite requires approximately 250 ms to retransmit the high level guardtone. Switches 150, 152 are configured to provide a binary encoded inputto the encoder circuit which activates an additional guard tone periodto be generated by the paging encoder. The high level guard tone signalcan be increased in 300 ms increments, and a maximum of 1200 ms can beeffected by switches 150, 152. If both switches 150 and 152 are open, nohigh level guard tone will be added to the normal tone sequence. Ifswitch 150 is open and switch 152 is closed, 300 ms of high level guardtone will be added to the initial tone sequence. Likewise, increments of300 ms can be added to the high level guard tone sequences by providingthe various combinations of switches 150 and 152.

The paging system encoder 14 is also configured to accept group andfunction tone select information through the keying mode select logic30. The keying mode select logic accepts switch input from severalsector select switches as well as a local key switch 154 and a threeposition mode switch 56. The keying mode and select circuit is shown inmore detail in FIG. 3b. The keying and mode select switches are userprogrammable and are located within the paging system encoder. Thevarious combinations of input switches are encoded in the keying andmode select logic which produces a plurality of station disable bits.The output of the keying and mode select logic circuit 30 is coupled to3 PIA circuits 132B which coupled the keying and mode station disablebits into microprocessor 144. The microprocessor 144 then generates theappropriate sequence of function tone disable tones based on the stationdisable bits. This will be described in more detail later. Referring nowto FIG. 3b, a detailed electrical schematic for a portion of the keyingand mode select logic circuit 30. The actual keying and mode selectlogic circuit consist of an array of the circuit shown in FIG. 3b and isdescribed in detail in Motorola instruction manual 68P81063E15-0entitles "Simulcast System Controller and Paging System Encoder" dated1982 and available from Motorola Communications Electronics, 1309 E.Algonquin Rd., Schaumburg, Ill.

The keying and mode select logic shown in FIG. 3b comprises a pair ofinverters 38 and 40 coupled to a pair of NAND gates 42 and 44respectively. These logic gate receive inputs through switches 32, 34and 36 located on a front panel. NOR gates 42 and 44 are coupled to NORgates 46 and 48 respectively. NOR gate 48 and 50 receive inputs from aswitch 56 which cooperates with two resistors 62 and 64. Eachtransmitter is instructed key or dekey based on these inputs by usingthe signals described in FIG. 3b, each paging remote transmitter can beassigned to a particular secter as well as a particular group. Thereforethe sector feature of the individual station control scheme does notdepend on the particular group or function tone assignment of the remotesimulcast station which are coupled to a power terminal 60. The outputsof NOR gates 48 and 50 are combined by NOR gate 52 which producesstation disable bits. The truth table for the logic circuit shown inFIG. 3b, is given below:

    ______________________________________                                        36         0 1 0 0 1 1 0 1 X                                                                            0=Logical Low                                       34         0 0 0 1 0 1 1 1 X                                                                            1=Logical High                                      52         0 0 0 0 0 0 0 0 X                                                                            X=Don't Care                                        54         1 1 0 1 0 1 0 0 1                                                  58         0 0 1 0 1 0 1 1 1                                                  SOBIT      1 1 0 0 0 1 0 1 1                                                                            (High-Disable)                                      ______________________________________                                    

In addition to the function described above the keying and mode selectlogic interfaces with several sector inputs 84, 86, 88, and 90 whichcooperate with switches 74, 76, 78 and 80. These inputs are combined bya NAND gate 82 and by diodes 66, 68, 70 and 72. These inputs indicate tothe keying and mode select circuit that as many as four sectors ofpaging transmitters should transmit.

Referring again to FIG. 3a the paging system encoder circuit cooperateswith the paging terminal 10 of FIG. 1, through the clear to page voiceterminal 162, the clear to page binary terminal 160, the key analogterminal 156 and the key binary terminal 158. In operation, a pagingsubscriber will activate the paging terminal 10 of FIG. 1, through atelephone link by signalling the telephone number assigned to the uniquepager address. The paging terminal 10 will then convert the telephonenumber to a signal comprising the exact pager address. The pagingterminal 10 then signals the paging system encoder that a paging signalis imminent by activating either the key analog terminal 156 or the keybinary terminal 158 depending on the type of pager being signalled. Ifthe key binary terminal is activated, the paging encoder will generatethe series of timed tones and pauses which instruct the remotetransmitter to key or not and place the paging remote transmitter sitein the binary transmission mode. When the transmitter has been properlyset up and keyed, the paging system encoder will activate the clear topage binary terminal, and activate the binary modem tone mute switch 118to pass modem tones to summing amplifier 126 and output transformer 136.Similarly, if the system is to be placed in the analog audiotransmission mode, the paging terminal will activate the key analogterminal 156 and the paging system encoder will generate the series oftimed tones and pauses which instruct the remote transmitter to key ornot and which place the paging remote transmitter in the analogtransmission mode.

FIGS. 4 through 16 are flow diagrams which define the operation of themicrocomputer 144 used in the encoder of FIG. 3. FIG. 4 details theoperation of the initial program sequence when power is first applied tothe paging encoder. Since it is not possible to predict a specific logiccondition which will be present at any particular input or outputterminal of the microprocessor or PIA, the power-up sequence of FIG. 4establishes known conditions on all critical input and output terminals.

When power is first applied to the paging encoder 14, the programcontrol of the microcomputer is configured to execute an initializationprogram 200. The program control then proceeds to item 202 andimmediately sets the microcomputer interrupt mask which insures theprogram will not be interrupted during the power-up sequence. Theprogram then initializes all random access memory variables.

The microcomputer 144 ports can be configured to function as eitherinputs or outputs to the microcomputer and must be configured accordingto program control. As noted in FIG. 3, the microcomputer 144 acts asthe tone sequence generator for the paging system encoder. Any toneswhich may be present at microcomputer port P2 of FIG. 3 are shut offduring the power-up sequence 200 by designating port P2 as an input.This step insures no tones are placed on the output of the encodercircuit until necessary.

The microcomputer 144 provides an internal tone generator which iscontrolled according to the state of an internal register. By entering anumerical value in the timer control and status register, acorresponding tone period will be generated by the tone circuit.According to the next item 206, the timer control and status registerare initialized and subsequently, an arbitrary number is loaded into theTCS register.

The power-up sequence next designates the PIA ports as input or outputs.

Referring now to FIG. 3, signals KA, KB, HO1, HO2, TT and OA are coupledto PIA port A. Likewise, signals CTPA, CTPB, MO, M1, M2, M3, AT1, AT2are coupled to PIA port B. In accordance with the present invention,FIG. 4 shows the PIA port configuration. Consequently item 210configures PIA port A as an input and PIA port B configures as anoutput. The power-up sequence next initializes the values associatedwith PIA port B by placing the code on the PIA port B 218 whichcorresponds to opening or inhibiting all mute switches 118, 120, 124,125 of FIG. 3, inhibiting the clear to page signals 160, 162 of FIG. 3and by adjusting the programmable attenuator 140 of FIG. 3 for maximumattenuation.

The paging system encoder makes decisions as to what subsequent actionsto effect based on two integral system status Bytes which are anindication of the system's past and present activity. The system statusbytes are designated New Status (NSTAT) and Old Status (OSTAT). Sincethe system operation will be affected by the old system status, forinstance an analog to binary transition, this byte must be initializedduring the power-up sequence. Item 220 sets the system status byte OSTATto a code comprising all binary ones, which indicate that the system iscurrently dekeyed.

The paging system encoder is now configured with initial conditions incritical areas which will ensure correct system operation. Subsequently,the interrupt mask is cleared 222, thus allowing the microprocessor toexecute interrupt commands. Timeout period 224 is provided to allow allinitial conditions on the system to stabilize. The paging encoder nowenters the SCAN mode 300.

Referring now to FIG. 5, there is illustrated a flowchart embodying thescan method of the present invention. The flowchart in FIG. 5 provides adetailed description for the process steps necessary for implementingthe scan method of the present invention in the paging system encoder 14in FIG. 3. The scan routine forms the basic background operating schemeof the present invention. The primary task for the scan routineinterprets key input commands from either hardware front panel switchesor from the paging terminal and exits to one of five tasks depending onthe condition of the key switches.

When the scan routine is activated, item 302 retrieves the system statusbits D6 from the system status bytes NSTAT and OSTAT.

Referring now to decision 306, if both system status bytes NSTAT andOSTAT show a binary 1 in D6, which is an indication of the hardwarepanel key switch, then the system is dekeyed, and program will enteritem 304. If either data bit D6 from NSTAT or OSTAT is a binary zero,the hardware panel key switch has been changed and the program willenter the panel key handler (PKHNDL) routine 308. Item 304 retrieves thesystem status bits D1 and D.0. from the system status bytes NSTAT andOSTAT. Status bits D.0. and D1 of NSTAT indicate whether the pagingsystem encoder is being signalled, that is either an analog or binarypaging signal is imminent from the paging terminal 10 or modem 12 ofFIG. 1. Decision 310 then compares system status bits D1 and D.0. whichindicate if a key command has been received from the paging terminal. IfNSTAT has not changed from the previous period OSTAT, the programreturns to the initial item of the scan routine and continues searchingfor a change.

If NSTAT has changed the system will enter item 316, which provides a 5ms time delay. This time delay provides enough time to detect a keybounce or an erroneous input. Decision 318 compares the key bit D.0. orD1 with the state of the key bit D.0. or D1 5 ms earlier. If a keybounce is detected, decision 318 returns program control to the firststep of the scan routine.

If a key bounce was not detected, the program proceeds to decision 320which examines the D.0. and D1 status bits in the OSTAT status byte. Ifthe D.0. and D1 status bits show 00 which is an impossible condition atthis point in the program, the program control will exit decision 320and proceed to error routine 334. If an error is not detected theprogram proceeds to decision 322. If the system has been previouslykeyed in either the analog or binary mode, the program will proceed todecision 326. If the system was not previously keyed, the program willexit the scan routine and proceed to the select modulation (SELMOD)routine 370, which will be discussaed in more detail later.

As noted previously, if the paging system has been previously keyed theprogram will proceed to decision 326. At this point, the paging systemwill either dekey or change transmission modes.

If the system status bits D1D0 of NSTAT and OSTAT indicate the sytem waspreviously keyed and is now required to dekey the program will proceedto the dekey routine 330. Alternatively, if the system status bits D1D0of NSTAT and OSTAT indicate the system should remain keyed, but inanother mode, the system will enter the modulation change routine 328.

The modulation change routine 328 occurs in mixed paging systems whenbinary pages are sent immediately after a tone-signalled page or visaversa. As previously discussed, mode information is carried on thesystem status bits D1D0. Item 352 retrieves the NSTAT status bits D1D0.Item 352 compares the NSTAT status bits with the OSTAT status bits. Ifthe NSTAT status bits D1D0 are both equal to binary zeros, a racecondition or overlapped key request is indicated. Decision 354 will thenpass program control to item 356 which will then update the NSTAT statusbyte to the current valve of OSTAT and subsequently select the statusupdate routine (REPOLL) 346.

If either NSTAT or OSTAT contains a binary one in D1DO, the program willproceed to decision 360. If the OSTAT status bits D1D0 show 10 and theNSTAT status bits show 01, an analog to binary transition is indicated,and decision 360 will select the AUDBIN routine 362, which will bediscussed in more detail later. If AUDBIN is not selected, the programwill proceed to decision 364. If the OSTAT status bits D1D0 show 01 andthe NSTAT status bits show 10, decision 364 will select the binary toanalog transition routine (BINAUD) 368. If BINAUD is not selected, anerror has occurred and decision 364 will select the error routine 334.

If the error routine 334 is selected, item 332 will reset the NSTATstatus byte value to the normal value (D1D0=11) indicating the systemshould be dekeyed. The Item 332 then selects the dekey routine 330.

When invoked, dekey routine 330 will execute the tasks required to dekeyor turn off the paging transmitter stations and reset the paging encoder14 for the next key-up sequence. The dekey routine begins with item 338which designates microcomputer port P2 of FIG. 3 as an input, thusturning off any tone appearing on the port. The program proceeds toitems 340 and 342 which updates the PIA port B bit status instruction sothat the audio mute switches 118, 120, 124 and 125 of FIG. 3 are set tomute the signal paths, and so that the programmable attenuator is setfor maximum attenuation. The program proceeds to item 344 which providesa waiting period required by the paging system to dekey. Item 344 thenproceeds to the REPOLL routine 346. This routine is the end of thebackground loop. It updates the current status of the paging systemencoder. Item 348 replaces the contents of the OSTAT register with theNSTAT status values, and then returns the program to the beginning ofthe SCAN routine 300.

Referring now to decision 322, if the system status bits indicate akey-up condition, the program will proceed to the modulation selectionroutine, SELMOD, routine 370. FIG. 5b shows the program sequence forSELMOD. The SELMOD routine 370 selects one of two sequencing tasks to beperformed by the paging system encoder, depending on the system statusbits D1D0 which indicate the key analog and key binary signals of thepaging terminal. Item 374 reads the NSTAT status bit for any keyingactivity. If both status bits D1D0 are binary zeros, a race condition isindicated, and decision 376 will select Item 378 giving binary priorityif both analog and binary key requests are simultaneous. Item 378 willupdate the NSTAT variables D1D0 to a 01 condition and select the key binroutine 386.

If the NSTAT variables D1D0 show a non-zero condition, a decision 376will select decision 380. If the system status bits D1D0 indicate ananalog page, decision 380 will select the KEYAUD routine 382. If KEYAUDis not selected, the program will select decision 384. If the systemstatus bits indicate a binary page, decision 384 will select the KEYBINroutine 386. If KEYBIN is not selected, decision 384 will select errorroutine 334.

Referring now to FIG. 6, there is illustrated a flowchart embodying thepanel key handler routine (PKHNDL) of the present invention. The PKHNDLroutine 308 is used anytime the hardware panel key switch is activated.PKHNDL 308 begins with decision 402 which examines the NSTAT and OSTATD6 status bits for any change. If no change is detected, decision 402selects the Repoll routine 346. If a change is indicated, decision 402will select item 406 which generates a 5 ms time pause in the program.Decision 410 examines the D6 data bit for a key bounce. If a key bounceis detected, program control will be returned to the SCAN routine 300.If a key bounce is not detected, the program proceeds to decision 412which selects item 416, if a dekey command has been detected. Item 416then clears the clear-to-page inhibit flag, and the program proceeds tothe ERROR routine. No real error has occurred here, but the ERRORroutine provides a proper status reset for a panel key operation.

If a dekey command is not detected, decision 412 will select item 414,sets the clear-to-page inhibit flag and sets the test tone sequence tostep O. Item 418 then sets the programmable attenuator 140 and audioswitches 118, 120, 124 to the mute condition. Item 422 then provides a500 millisecond time delay before selecting the KEYAUD routine 382,since a hardware panel key can only activate the analog mode.

FIG. 7 shows a flowchart embodying the analog key-up routine (KEYAUD)382 of the present invention. KEYAUD 382 is selected when the pagingsystem encoder is to key up in the analog mode. KEYAUD sequences thetone attenuator, calls the tone sequencer and opens the tone and audiosignal paths. It then signals the paging terminal when the paging systemis clear to page.

When selected, KEYAUD proceeds to item 450 which selects the high levelguard tone subroutine (HLGT) 450. HLGT causes the high-level guard tonesequence to be placed at the output of the paging encoder. This will bediscussed in more detail later. When completed, HLGT returns programcontrol to item 452 which adjusts the programmable attenuator 140 ofFIG. 3 for mid-level attenuation. The program proceeds to item 392 whichcalls the group 1 routine described in FIG. 11a. Item 394 then selectsthe group 2 routine described in FIG. 11b. Item 396 then selects thegroup 3 routine described in FIG. 11b. Item 454 then sets the ENCINC ortone generator register to produce the function tone frequency. Item 456and decision 458 cause the function tone to be produced by themicroprocessor for 40 ms. When the function tone period has elapsed, theprogram will proceed to item 460 to generate a guard tone signal.Program control proceeds to item 480 which reads the PIA switch byte forfunction tone and transmit inhibit information. The station requiresthat the line PTT stay keyed in the analog mode. During long functiontone strings the line. PTT signal becomes inactive since HLGT is notpresent for more than 1 second. Decision 482 and Items 484 and 490produce an additional period of HLGT. If a transmit inhibit was notdetected, program control will proceed to item 488 which increments thePIA address and selects decision 486. If the last address is notindicated item 480 will be selected otherwise, the program would thenselect item 462 which adjusts the programmable attenuator 140 of FIG. 3to a low level corresponding to the level required by the low levelguard tone. Subsequently, item 464 opens mute switch 120 correspondingto the audio paging tones, and item 466 opens the remaining two muteswitches. Decision 468 examines the clear to page inhibit flag. If theclear to page inhibit flag is set, because of a hardware panel key, thedecision 468 will select the REPOLL routine 344. If the clear to pageinhibit flag is not set, decision 468 will select item 470 which enablesthe clear to page analog line and inhibits the clear to page binaryline.

Referring now to FIG. 8, there is illustrated a flowchart embodying thebinary key routine (KEYBIN) of the present invention. When activated,KEYBIN proceeds to item 500 which calls the HLGT routine 450. Whenexecuted, HLGT will return program control to item 502 which adjusts theprogrammable attenuator 140 of FIG. 3 for mid-level attenuation. Theprogram proceeds to item 392 which calls the group 1 routine describedin FIG. 11a. Item 394 then selects the group 2 routine described in FIG.11b. Item 396 then selects the group 3 routine described in FIG. 11b.The program then proceeds to item 504 which adjusts the ENCINC registerto produce the function tone frequency. Decision 508 causes this tone tobe placed at the output of the paging encoder for 40 ms. The programthen executes item 510 which sets the programmable attenuator 140 ofFIG. 3 and mutes attenuator mute switch 125.

Item, 520 then designates microcomputer port P2 as an input, thusinhibiting any tone output from the microprocessor. Item 522 anddecision 524 then cause the microprocessor to pause for a time period sothat a 150 ms. pause will appear at the output of the paging encoder.When 150 ms. has elapsed, item 526 sets the "comma" counter for thedesired number of comma cycles, and Item 528 calls the comma routine528. This will be discussed in more detail later. The program thenproceeds to item 530 which enables the clear to page binary line,inhibits the clear to page analog line and opens the binary modem tonesignal path. The program then selects the REPOLL routine 346.

Referring now to FIG. 9, there is illustrated a flowchart embodying thehigh-level guard tone (HLGT) routine of the present invention. Thehigh-level guard tone signal signals a paging transmitter site that apaging signal is imminent and the transmitter should turn on. In asystem which uses link stations to connect the remote stations,additional periods of high-level guard tone are required to allow eachstation along the link to receive the high-level guard tone frequency.

The HLGT routine begins with item 550, which reads the NSTAT Hop selectdata bits D2D3 which reflect the user selectable internal hardwarecondition of switches which provide information as to how many linktransmitters are in use and subsequently, what time period of high-levelguard tone is required. The program then proceeds to item 552 whichadjusts the ENCINC register to generate a guard tone frequency. Item 554then adjusts the programmable attenuator 140 of FIG. 3 for high level orminimum attenuation and then opens the microcomputer tone mute switch125. Item 556 then designates microprocessor port P21 of FIG. 3 as anoutput, thus enabling the tone output of the microprocessor. The programthen proceeds to decisions 558, 560, 562 which examine the NSTAT statusbits D2D3 to determine the number of HLGT periods required. If noadditional guard tone is required, decision 558 will select item 570which will cause HLGT to be generated for 120 ms. Similarly, if onetransmitter hop is required, decision 560 will select item 572, whichwill cause HLGT to be generated for 420 ms. If two hop periods arerequired, decision 562 will select item 566 which will cause HLGT to begenerated for 720 ms. Otherwise, item 564 will be selected, and HLGTwill be generated for 1020 ms. Decision 568 examines items 570, 572, 566or 564 and evaluates the elapsed time depending on which item wasselected. When the HLGT sequence has elapsed, decision 568 will returnthe program control to the subroutine which selected the HLGT routine.

Referring now to FIG. 10, a detailed flow diagram for the function tonegenerator and sequencer (SEQ) utility module is shown. SEQ 850 beginswith item 852 which establishes a pointer index value of zero. Theprogram proceeds to decision 854 which progressively checks each PIAbit, that has been set by the circuitry shown in FIG. 3b, to determineif the corresponding transmitter should be disabled. If the transmitteris disabled, program control proceeds to item 862. Item 862 andsubsequent items form the function tone generator. Item 862 begins togenerate a function tone and program control passes to item 864. Item864 examines an internal microprocessor timer and in cooperation withdecision 866 causes the function tone to be generated for approximately40 milliseconds. Program control then proceeds to item 856. Returningnow to decision 854, if the tramsmitter was not disabled, programcontrol proceeds directly to item 856 which increments the index.Decision 858 then examines the index. If less then ten PIA bits havebeen checked, program control returns to decision 854 to determine ifsubsequent transmitters should be disabled. If all ten bits for theparticular group have been checked, program control returns to thesubroutine which activated the SEQ routine.

Referring now to FIG. 11A, the group 1 subroutine described in FIG. 5 isshown. Group 1 392 begins with item 890 which reads the PIA 132B inputsas shown in FIG. 3. Item 890 searches this PIA information fortransmitter disabled status. Item 892 is then selected which follows thesequence subroutine as described in FIG. 10. Program control thenreturns to the subroutine which activated group 1 either KEYAUD 382 asshown in FIG. 7 or KEYBIN 386 as shown in FIG. 8.

FIG. 11B shows group 2 subroutine 396 described in FIG. 7. Group 2begins with item 898 which reads the second section of PIA 132B as shownin FIG. 3 for transmitter disable status. The program then proceeds todecision 898. If all transmitters are to be keyed, program controlreturns to the subroutine which activated the group 2 routine. Ifcertain transmitters are to be disabled, program control proceeds toitem 900 which generates keying sequence tone two. Item 902 and decision904 cause the keying sequence tone to be generated for 40 milliseconds.When the 40 milliseconds time has elapsed, item 906 selects the sequenceroutine of FIG. 10. Program control then returns to the subroutine whichactivated the group 2 routine.

Referring now to FIG. 11C, there is shown a detailed flow diagram forthe group 3 routine 394 as described in FIG. 7. Group 3, 394 begins withitem 910. This module determines which transmitters in group 3 of thesimulcast sytem are to be keyed by reading the select inputs from asection of PIA 132B as shown in FIG. 3. It then generates a keyingsequence tone and then calls the function tone sequence routine (SEQ) togenerate the required tone sequence. Also, if no function tones weresent in group 2, keying sequence tone 2 is also sent. Item 910 reads PIAtransmitter select inputs for group 2 information. If the group 2information indicates that no transmitters in group 2 transmitted duringthe last cycle, decision 912 selects item 914 which generates keyingsequence tone 2. If the group 2 information indicated that a transmitterhas been keyed in group 2, program control proceeds directly to item 916which reads PIA 132B for group 3 information. Program control proceedsto decision 918. If all transmitters are to be keyed in group 3, programcontrol proceeds directly to the subroutine which selected the group 3routine. If every transmitter is not to transmit within the group 3group, program control proceeds to item 920 which generates keyingsequence tone 2. Item 922 in decision 924 cause the keying sequence toneto be generated for approximately 40 milliseconds. Item 926 then selectsthe sequence subroutine described in FIG. 10. Program control thenpasses to the subroutine which accessed the group 3 routine.

Referring now to FIG. 12, there is illustrated a flowchart embodying thebinary comma generator routine (COMGEN) of the present invention. COMGENgenerates a burst of (N) mark-space modem tone sequences of standardtone frequencies at 1200 Hz or 2200 Hz for asynchronous modems.

COMGEN begins with item 700 wh1ch disables all clear-to-page signals,opens the modem tone mute switch 118 of FIG. 3 and adjusts theprogrammable attenuator 140 of FIG. 3 for mid-level attenuation. Theprogram then proceeds to item 704 which instructs the microprocessor togenerate a 1200 Hz signal by loading the ENCINC register and designatingmicrocomputer port P2 as an output. Item 706 then generates a timeperiod which causes the 1200 Hz signal to be generated or 1.6667 ms.This signal comprises a FSK binary one. The program then proceeds toitem 708 which instructs the microprocessor to generate a 2200 Hz signalby addressing the ENCINC register item 710 and then causes the 2200 Hzsignal to be generated for 1.818 ms. This signal comprises a FSK binaryzero. When this time has elapsed, item 712 will decrement the commacounter which was initialized by the routine utilizing the COMGENroutine. Decision 714 examines the comma counter register. If the commacounter is currently a non-zero value, decision 714 will return programcontrol to item 704. If the comma counter contains a zero value, theprogram will proceed to item 716 which designates microcomputer port P2as an input, thus inhibiting the microprocessor tone generator. Item 716also closes the attenuator mute switch, disables all clear-to-pagesignals and sets the programmable attenuator or maimum attenuation. Item718 then returns program control to the routine which activated COMGEN.

Referring now to FIG. 13, there is illustrated a group of flowchartsembodying the time delay generator routines of the present invention.These routines are utilized whenever the microprocessor is required togenerate tones or pauses for a specific period of time, as well as anyother task which requires a timekeeping function.

FIG. 13a shows a flowchart illustrating the timer set routine TSET whichis called by background routines anytime an elapsed time timer is to beset up. The microprocessor 144 of FIG. 3 utilizes a 16-bit free-runningcounter register (FRR) to generate time information. In addition, asecond 8-bit register (TIME) is utilized. Whenever the free-runningregister contains all binary one's, an overflow will activate the TOFINinterrupt routine which will increment the value stored in TIME.Therefore, subsequent overflows will be accumulated in TIME via theTOFIN interrupt routine.

The TSET routine 750 begins with item 752 which saves the values storedin FRR and the index register. The program proceeds to item 754, andcaptures the present time as indicated by the value of FRR. Item 756then retrieves the required time delay value and adds this value to thevalue stored in FRR. This target value will be an indication of thevalue of FRR when the desired time has elapsed. Item 758 then restoresthe registers and stores the computed time in a target register,(TARGET), and program control returns to the routine which activatedTSET.

FIG. 13c illustrates a flowchart showing the timer interrupt overflowroutine (TOFIN) of the present invention. This routine is entered everytime the value stored in FRR increments to a value represented by abinary one in every bit of the register.

TOFIN begins with item 770 which clears the timer overflow interruptflag allowing the timer to generate an interrupt during the subsequenttimeout. Item 772 then increments the value stored in TIME. Item 774then services the watchdog timer. The watchdog timer is a hardwaredevice which prevents runaway conditions in the microcomputer 144. Ifthe watchdog timer is not addressed within a predetermined period, thetimer will reset the microprocessor. The watchdog timer prevents runawayconditions in the microcomputer. Item 774 will then return programcontrol to the routine being executed when the interrupt occurs.

FIG. 13b shows the timer compare interrupt handler routine (TONOUT)which generates a square-wave signal, and is used for tone encoding.TONOUT generates a tone frequency based on the value stored in theENCINC register. TONOUT can generate frequencies which range from 300 to3000 Hz.

TONOUT is activated anytime the value of an internal register (TCOMPR),related to the value of ENCINC, is equal to the value of thefree-running register. When the TCOMPR value is equal to the value ofthe free-running register, an interrupt will activate TONOUT 760. Item762 will then toggle the microprocessor port P21. Item 764 then updatesthe TCOMPR register to generate an interrupt a half period later. Item764 subsequently returns the program control to wherever the program waswhen it was interrupted.

Referring now to FIG. 14, there is illustrated a flowchart embodying thetimer check routine TCHK of the present invention. The TCHK routinedecides whether the timer interval, previously established by the TSETroutine, has elapsed. It is called by the background routines whichutilize the target parameter of FIG. 13. TCHK captures the present timefrom TIME and the MS byte of FRR in Items 804 and 812. Item 802 savesthe TARGET time value.

Items 816 through 856 test present time compared to TARGET time. Ifpresent time equals or exceeds TARGET, TCHK returns control to thecalling routine with carry bit set. Otherwise control is returned withCarry Clear.

The mathematics of checking for "greater than" or "less than" iscomplicated by the fact that the incremented TIME value will eventuallyset the most significant bit. Once set, TIME is considered a negativenumber for math functions and would test as "less than" the TIME valuejust before the MSB was set. Much of the logic discussed below dealswith reconciling this anomaly.

TCHK 800 begins with item 802 which saves the values contained in theindex and target registers and sets the interrupt mask 804. Item 804retrieves the value stored in the TCSR register and also retrieves thevalue of the TIME register most significant bit. If these valuesindicate that an interrupt which would activate TOFIN is pending,decision 806 will select item 808 which increments the value stored inTIME and resets the watchdog timer. The program will then proceed toitem 812. If an interrupt is not pending, decision 806 will select item812 directly. Item 812 retrieves the value stored in TIME, and item 814clears the interrupt mask.

Decision 816 compares the values of the previously stored TARGET andTIME registers. If the values stored in TIME have the same sign theprogram will proceed through decision 818. If the target value is alsopositive decision 818 will direct program control to TSAME by selectingitem 836, which calculates the differnce between the TIME and TARGETregisters. If TIME minus TARGET is greater than zero, decision 838 willreturn program control to the subroutine which selected TCHK. If thevalue of TARGET minus TIME is less than zero, the program proceeds tothe NOTYET routine 842 by selecting item 844. Item 844 clears the carrybit of the free running register FRR. The program then proceeds to item848 which resets the watchdog timer and restores the TARGET and indexregisters and returns program control to the subroutine which selectedTARGET.

Referring back to decision 818, if the value stored in time is positive,and the value stored in target is negative, decision 818 selects item822 which calculates a new value for TIME based on an estimate of themaximum amount of time which could have elapsed since the routine wasactivated. This new value is known as the latency period. If the newvalue of TIME is still positive, the routine will select NOTYET 826. Ifthis new value of time is now negative, the program will proceed toCOMMON 828. Referring now to decision 816, if TIME is negative, theprogram selects decision 830. If the value stored in TARGET is negative,the program proceeds to TSAME 832. If the value stored in TARGET ispositive, decision 830 will select item 834, which calculates a latencyperiod in eactly the same manner as item 822. Item 834 then proceeds todecision 840 which evaluates the new value of time.

If the new value of TIME shows a negative value, the program willproceed to NOTYET 842. If the new value of TIME is positive, decision840 will select COMMON 828.

COMMON 828 begins with item 850 which calculates a value equivalent toTIME-TARGET. The program then proceeds to decision 852. If the newcalculated value is negative, decision 852 selects item 856 which setsthe carry bit and then selects the RET routine 846. If the newcalculated value is positive, decision 852 selects the NOTYET routine826.

FIG. 15 shows a block and circuit diagram for the paging remote stationsystem decoder that is responsive to the signalling scheme described inFIG. 2. A more detailed electrical schematic for the remote stationdecoder is illustrated in Motorola document 68P8106E70, published May,(1982) entitled "PURC Paging Stations" available from the ServicePublication Department of Motorola, Inc., 1301 East Algonquin Rd.,Schaumburg, Ill., or from Motorola C & E Parts, 1313 East Algonquin Rd.,Schaumburg, Ill. The decoder receives the page information from a localor remote terminal at line drive 101. The station is first keyed up whenthe decoder receives the guard tone-function toner signal from theterminal. The line driver 101 receives the guard tone-function tone anddirects it to guard tone decoder 103. The guard tone decoder 103 detectsthe guard tone frequency and sends a signal A to relay 107 and thestation controller 105 which in turn outputs a signal B to a digitalmodulator 109. Upon detection of a high level guard tone by the guardtone decoder 103, the guard tone decoder enables function tone window103a which allows the function tone to pass to the function tone decoder201. Upon detection of the function tone, the function tone decoder 201generates an output signal C which is delivered to channel element 203which activates the channel element in preparation for transmission of asignal. A second output from the function tone decoder provides a signalD to the station controller 105. Signal D tells the station controllerto key the exciter in the transmitter and thereby fully enable the basestation transmitter. Therefore, upon receipt of signal D, the stationcontroller 105 sends a signal E to turn on exciter 205.

Signal A from the guard tone decoder 103 causes relay 107 to open andthus place modem 207 offline. Signal A will be removed from relay 107and signal B is removed from digital modulator 109 at approximately130-150 milliseconds after loss of guard tone. Since all analog data issummed with a control tone that corresponds to the guard tone frequency,signal A from guard tone decoder 103 will continue to be applied to thestation controller 105 as long as analog data and its guard tone carrierare detected. Therefore, signal A will continue to hold open relay 107for the duration of guard tone plus an additional time period ofapproximately 130-150 milliseconds. The function tone decoder 201immediately thereafter disables the function tone window 103a withsignal F.

After the guard tone decoder 103 ceases to detect a guard tone, signal Awill be removed from the delay enable of station controller 105 withinapproximately 70 ms. Any further signals received by the line driverfrom the remote or local terminal will now be seen by the modem 207. Themodem 207 will convert the audio FSK received from the terminal to ashifting DC voltage which serves as an input to the transmitter siteinterface 209.

When the remote transmitter site interface 209 detects active data(active since the modem will consider guard tone as a static data) itwill generate a data detect signal G which opens or disables thetransmit audio path by way of FET 301. The transmit audio path isdefined by amplifier 303, notch filter 305. The notch filter 305 servesto notch out the guard tone frequency. The data detect signal G willremain as long as the transmitter site interface continues to receivebinary data from modem 207. Signal G also disables or inhibits the guardtone decoder 103 in order to prevent the falsing of signal A and inaddition causes signal B to be applied to digital modulator 109. Thetransmitter site interface 209 passes the binary data to the digitalmodulator 109 which modulates the binary data to produce a frequencyshift keying-non-return to zero output (FSK-NRZ). The FSK output isapplied to the input of element 203 to be transmitted by the basestation.

If a voice message is to follow the binary information, another timeperiod pause of approximately 50 milliseconds is introduced into thesignalling scheme as described in connection with FIG. 2. This 50millisecond time pause allows the transmitter site interface 209sufficient time to remove the signal G from the FET 31 and stationcontroller 105 and guard tone decoder 103. Therefore, after binary datais no longer detected by the transmitter site interface 209, the datadetect signal G is removed over approximate 50 millisecond time period.Immediately thereafter, a high level guard tone is again sent to thedecoder and detected by the guard tone decoder 103. This causes signal Ato be applied to the relay 107 and station controller 15 which in turncauses signal B to be applied to digital modulator 109.

Immediately after the high level guard tone is received, the analogsignal on the guard tone carrier is received. The guard tone carrierkeeps signal A from guard tone decoder 103 present at the delay input ofstation controller 105. The presence of low level guard tone keepssignal A applied to relay 107 for the duration of the voice plus the130-150 millisecond time delay. The voice message is transmitted throughthe audio path and stripped of the guard tone carrier at notch filter305. At the completion of the voice message, the guard tone decoder 103no longer receives and detects a guard tone and therefore signal A tothe station controller 105 and relay 107 is removed.

After the loss of signal A relay 107 is closed and the modem 207 is online to receive any binary data from line driver 101. Removing signal Bfrom digital modulator 109, the digital modulator begins a count ofbetween 275-325 milliseconds at the end of which signal H (which appearsimmediately upon the appearance of signal B) is removed from the stationcontroller 105 which causes signal E to be taken away from exciter 205.Thus, the station is dekeyed since it has not received any additionalbinary or analog information for a delay in signal H for 300 ms.

As long as any of the signals D and H appear at the station controller105, the output signal E will keep the exciter 205 enabled and thus thebase station transmitter keyed up. By the appropriate delay indeactivating signal B, the station controller 105 provides the decoderability of interactively handling binary pages and analog pages withanalog voice.

FIG. 16 shows a detailed electrical schematic of the function tonedetector module 201 of FIG. 15. The function tone detector consists of abuffer register 111 which interfaces between a microprocessor 113 andthe various transmitter keying control inputs. A second buffer register123 connects between the microprocessor 113 and the paging transmittercontrol unit of FIG. 15. As noted in FIG. 15, the function tone detectorcontrols the simulcast transmitter output through the buffer 123outputs. The microprocessor 113 also interfaces with a bank of userprogrammable switches which are used to select group and function toneidentity for a particular simulcast remote site. The microprocessor 113cooperates with an address decoder 115 and the user programmable dipswitches through the buffer 117. The microprocessor 113 also cooperateswith a watch dog timer 121 which monitors the microprocessor forabnormal program conditions.

The detailed operation of the microprocessor 113 is defined by the flowdiagrams shown in FIGS. 5 through 16. In general however the functiontone detector 201 receives incoming function tone signals through buffer127. These function tone signals are analyzed to determine if a validfunction tone sequence has been received. If no valid function toneshave been received the microprocessor will examine the various PTcontrol signals and if instructed to do so, will key the transmitterwith the appropriate control signals.

If a valid function tone sequence has been received, the function tonedetector will prevent the simulcast remote station from transmitting.

Referring now to FIG. 17, there is shown a structure diagram definingthe hierarchical relationships between the various program routines usedin the function tone detector shown in FIG. 16. Upon initial activation,the decoder of FIG. 15 will first activate the reset module whichinitializes the simulcast control module at power-up time. It sets thesignalling state to search for a line push-to-talk (A) and passescontrol to the background loop EXEC module 303. The EXEC module 303 isthe underlying simulcast control module and background routing module.This module schedules and calls the background task subroutines thatmake up the background subroutines that make up the background loop. Italso calls the signalling state handler modules which are determined bythe value of several of the bits in the state variable byte. If a newstate is being entered, the set-up routine for the particular state iscalled first. After this, other utility background routines are called,and then the whole process repeats indefinitely. Program control passesfrom the exec module to any of the other six handler modules. Programcontrol can pass from the EXEC module 303 to PTT module 305, to thefunction tone decode handle module 307, to the function tone executormodule 309, to the key-up handler 311, to the line push-to-talk lock-updelay handler 313, or to the simulcast control wait de-key handlermodule 315. These modules will be discussed in more detail later.

Referring now to FIG. 18, there is shown the reset module 301 of FIG.17. The reset module 306 initializes the simulcast control module atpower-up time. It sets the signalling state to search for linepush-to-talk and passes program control to the background EXEC module.The reset module 301 begins with item 353 which sets the microcomputerinterrupt mask to prevent interrupt from occurring during the resetpower-up sequence. Program control then passes to item 357 whichinitializes the stack pointer. Item 359 then initializes all the RAMvariables in conjunction with decision 361 which continuously clears allRAM locations until every memory location has been cleared. After theRAM variables have been initialized, program control passes to item 357which defines PIA ports as outputs.

FIG. 19 is a detailed flowchart of the background EXEC module whichexamines the current state of the individual station control decoder andmakes a determination which of the six utility modules should be invokedduring the next cycle. EXEC 303 begins with item 375 which examines amemory location which indicates whether EXEC has been previouslyinvoked. Program control proceeds to item 327 which recalls the statevariable which defines the current status of the individual stationcontrol decoder. Item 379 then calculates which version of the sixutility modules should be invoked based on whether the utility modulehas been previously invoked or not. Decision 381 examines the statevariable. If the state variable indicates that the utility has notpreviously been invoked, program control proceeds to item 383 whichupdates the state variable to indicate that the utility has been invokedand then proceeds to item 385 which calls initialization subroutine foreach of the six utility modules. If the the utility module has beenpreviously invoked, program control will proceed to item 387 which willpass program control to whichever utility subroutine was indicated bythe state variable. Item 389 then resets the watchdog timer bit asprogram control passes to EXEC.

FIG. 20 shows a detailed flow diagram for the PTT utility subroutine 305shown in FIG. 19. The PTT subroutine module scans the decoder portinputs for a line push-to-talk signal, a local push-to-talk signal or aremote push-to-talk signal as shown in FIG. 16 and sets the CPU statevariable to key up the transmitter or to prepare to receive a functiontone, i.e., enable the function detector according to the inputsreceived. The PTT subroutine is a two-pass routine. That is, on thefirst pass, PTT 305 begins with item 395 which utilizes the ports P14and P17 as outputs. Then program control returns to the EXEC routineshown in FIG. 19. On the second and subsequent passes, program controlwill proceed directly to PTT plus 3 (401) in FIG. 9.

FIG. 21 shows a detailed flow diagram for the PTT+3 routine. PTT+3begins with item 403 which reads the appropriate PTT inputs from the PIAport, and item 405 stores this information in a RAM location. If noactivity has been indicated, program control will return to the EXECsubroutine of FIG. 19 through item 409. If activity has been indicated,item 411 generates a 5 ms time delay for the purposes of detecting aswitch bounce. Item 413 then reloads the PIA inputs and compares withthe values received before the 5 ms delay. If these values do not agree,i.e., if a switch bounce has been detected, decision 415 will passprogram control to item 419 which resets the state variable to zero andclears the state flag. Item 419 then passes program control to thebackground exec module of FIG. 19. If the switch bounce was notdetected, decision 417 examines the PIA inputs and decides if the localPTT signal or PTT control signal has been detected. If so, item 421 setsthe state variable equal to three, clears the flags and returns programcontrol to the background exec module. If a PTT has not been indicated aline PTT is indicated and, decision 417 passes program control to item423 which sets the state variable equal to one, clears the flags andreturns program control to the background EXEC module 303 of FIG. 19.

FIG. 22 shows a detailed flow diagram for the function tone detectprogram module (FTD) 307. This module handles background tests for thefunction tone decode state which is associated with state one of thestate variable. This state is entered into after a high level guardtonehas been detected. It enables the function tone decode foreground taskand locks down the line push-to-talk signal. The system will stay inthis state until a function tone is received. If an invalid tone or atime-out condition occurs, the system will return to the PTT decodestate. If a valid tone is received, the system will move on to thefunction tone execute state which is associated with a value of two forthe state variable. The FTD module is also a two-pass subroute. If FTDhas not been accessed by the EXEC module earlier, the system will accessthe first entry point to FTD 307 which begins with item 427 which setsan interrupt mask to prevent an interrupt while FTD is active. Item 429then enables an internal microprocessor input associated with aninternal timer and stores the value of the current timer state. Item 431then clears the function tone buffer of any existing information whileitem 433 initializes a tone status word (DSTAT) to zero indicating thatguardtone has been received and clears function tone foregroundvariables which are used to detect the presence of a function tone. Item435 activates the line push-to-talk control and enables the functiontone window control (F) of FIG. 15. Item 437 stores the value of acounter in a RAM location, and the program control proceeds to item 439which initializes an internal activity timer and passes program controlto item 441 which sets the function tone detect window timer. All of thefunction tone detect variables have been initialized at this point, anditem 443 clears the interrupt masks and passes program control back tothe background exec module 303 shown in FIG. 19.

DSTAT is generated and updated by a tone decoding foreground routine.This routine places a binary representation of the tone that has beendetected in four bits of DSTAT. The routine also sets a valid tone bitand an activity bit based upon preset limit values for detected tones.

FIG. 23 shows a detailed flow diagram of the FTD+3 utility module whichis accessed anytime FTD is indicated by the state variable and FTD hasbeen accessed previously to initialize the FTD variables. FTD+3 447begins with item 449 which recalls the tone detect status word DSTAT.The tone detect status word DSTAT provides an indication of whether atone has been detected, as well as containing a binary representation ofthe tone which has been detected. In other words, every simulcaststation decoder is equipped to decode as many as sixteen tones. If oneof these tones has been detected, its binary representation will bestored in DSTAT. Once the DSTAT status word has been accessed, programcontrol passes to decision 451 which examines the DSTAT status word. IfDSTAT indicates that a tone has been detected, program control proceedsto 455 which refreshes the activity timer and clears the activity anddetect flags. Program control then proceeds to decision 457 whichexamines the DSTAT status. If DSTAT indicates it is guardtone that hasbeen detected, program control returns to the EXEC subroutine. Ifguardtone has not been detected, item 461 searches for an empty bufferlocation in the function tone buffer. Decision 463 determines that thefunction tone buffer has been found. Decision 465 examines the tonestored in the particular FT location. If the tone in the function tonebuffer indicates this is the first tone, item 477 stores the tone into aselective function tone buffer location. If the tone is not the firsttone decision 465 proceeds to decision 469. Decision 469 examines thetone in the function tone buffer. If a duplication of the previous toneis indicated, then decision 469 passes program control to the backgroundEXEC subroutine shown in FIG. 19. If decision 469 indicates that this isnot a duplication with previous tones, then the tone is stored by item477. Decision 475 examines the tone stored in the function tone bufferlocation. If a final keying sequence tone is indicated, then programcontrol proceeds to item 479 which updates the state variable, adjustsit for a value of two and clears the state flag. If a keying sequencetone was not indicated, decision 475 returns program control to the EXECsubroutine. Returning to item 479, once the state variable has beenupdated and the state flag cleared, program control proceeds to the exitsubroutine 493.

Returning now to decision 451, if the DSTAT status byte indicates that atone has not been detected, program control proceeds to decision 453which examines the function tone time window interval to see if the timefor detecting a function tone has elapsed. If the time has not elapsed,program control proceeds to item 459 which checks the DSTAT status wordfor any new activity. If activity has been detected, decision 481 passesprogram function tone time window interval to see if the time fordetecting a function tone has elapsed. If the time has not elapsed,program control proceeds to item 459 which checks the DSTAT status wordfor any new activity. If activity has been detected, decision 481 passesprogram control to item 483 which refreshes the activity timer andclears the activity flag. Program control then returns to the EXECbackground subroutine. If activity timer time has elapsed, programcontrol proceeds to item 491 which re-initializes the state variable andclears the state flags and enters the exit subroutine 493. Exitsubroutine 493 begins with item 495 which disables the capture interruptand shuts off the function tone window controls. Program controlsubsequently reverts to the EXEC background subroutine. Returning now todecision 463, if an appropriate function tone buffer location cannot befound, program control passes to decision 467 which examines thefunction tone buffer for an overflow indication. If a function tonebuffer overflow is indicated, program control passes to the abortsubroutine 491 as discussed earlier. If a function tone buffer overflowis not indicated, program control returns to item 461 to continuesearching for an empty buffer location in the function tone buffer.

FIGS. 24A and B show the function tone executor module (FTX) 309. TheFTX module is invoked by the EXEC background subroutine when the statevariable has been set to 2. The function tone detector module causes thestate variable to be set to 2 when a valid sequence of function tones isreceived. Its purpose is to search this stack of function tone numbersand decide whether a valid transmitter knock down tone was decoded inthe stack. If so, the transmitter is inhibited, if not, the transmitteris set up for key-up. This module contains a first pass to decide whichof the functions tones to look for, and a second pass to find the propertone numbers.

According to FIG. 24A the first time the FTX module is activated, FTX309 begins with item 501 which reads the simulcast station controldecoder programming switches for function tone group information. Thisinformation is derived from switches within the simulcast decoder. Item503 then accesses the group information from the function tone groupswitches. The program proceeds to decision 505 which examines the groupinformation to determine if the particular simulcast station has beenprogrammed for group 0. If group 0 information has been detected, thegroup 0 subroutine 507 is invoked. The group 0 subroutine begins withitem 549 as shown in FIG. 24B. If group 0 is not detected the programcontinues to decision 509 which examines the group information todetermine whether group 3 information has been programmed into thestation control switches. If group 3 information has been detected, theprogram proceeds to item 511 which resets the group flag information andthen selects item 515. Item 515 sets the KT3 keying sequence tone as astart of group tone and sets KT1 as an end of group tone. The programthen proceeds to the function tone programmer routine (FINDFT) whichbegins at 519. Returning now to decision 509, if group 3 information wasnot detected, the program will proceed to decision 513. If group 2information is detected, the group 2 subroutine 512 will be invoked anditem 531 will set the group flag to zero and proceed to item 533 whichwill set keying sequence tone 2 (KT2) as a start of group tone and setkeying sequence tone 3 (KT3) as an end of group tone. The program willthen proceed to the FINDFT routine 519. Returning to decision 513, ifgroup 2 information was not detected, group one is indicated and item517 will set the group flag byte to $FF and establish keying sequencetone 2 as an end of group tone. The program will then proceed to FINDFT519.

The function tone programmer subroutine FINDFT begins with item 521.Item 521 loads the function tones information from the paging systemdecoder switches. Item 523 then sets the function tone frequency indexequal to the values indicated in the function tone switch information.Program control proceeds to item 525 which examines the simulcastprogramming switches for any activity and compares this activity withthe indicated frequency. Item 525 examines the first function toneswitch that is activated. If an active switch is detected, decision 527selects the found subroutine 529. If an active switch was not detected,decision 527 will select item 535 which will increment the frequencyindex for the next function tone frequency. Program then proceeds toitem 537. If an index overflow is not indicated, the program will againselect item 525. If an index overflow is indicated item 539 will beselected and the group flag will be set to $AA. Item 539 will thenselect subroutine SETTX 543. SETTX begins with item 545 which will setthe transmit flag to $$FF indicating a keyed-up condition which is thenormal state for a remote simulcast transmitter unless instructed tode-key. Item 547 will then return to the EXEC background routine shownin FIG. 19. Returning now to decision 527, if switch activity wasdetected, the found subroutine 529 will be selected which begins withitem 541. Item 541 is invoked when an active switch is found. This itemwill store the tone which has been found in a RAM location FMATCH formatchup with decoded tones which are fetched in the second pass of theFTX module. Item 541 then selects the SETTX routine 543.

FIGS. 25A and B show a detailed flow diagram for the FTX+3 subroutinewhich is invoked after the FTX routine has been invoked previously.FTX+3 matches the function tone selected in pass one with one of thetones in the stack received from the FTD module. FTX+3 begins with item549 which reads the current group flag information. Decision 551examines the group flag information. If the group flag status byteindicates group zero information, then a transmitter key-up isindicated, and the key-up subroutine 553 will be selected. If group zeroinformation is not indicated in the group flag status plate, decision551 will select item 555 which loads the current's function tone bufferpointer to the start of the function tone stack to search for the propergroup and knock-down tones. The program then enters the function toneloop 557 which begins with item 559 which begins by selecting the firstfunction tone. The program proceeds to item 561 which examines the firstfunction tone to determine if start of group tone has been detected. Ifa group start tone has been detected, the program will select item 563which will reset the group flag status byte to $FF and select the keyingsequence tone one check routine 567. If a start of group tone has notbeen detected, item 561 will directly select the keying sequence toneone check routine 567. Keying sequence tone check routine 567 shown inFIG. 13B begins with decision 597. Decision 597 examines the group flagto determine if the keying sequence tone detected is in the desiredprogramming group. If the group tone detected is equal to $AA, theprogram will proceed to the ABORT subroutine 599 or return programcontrol to item 565 based on the condition of the group flag. If thegroup tone detected was in the desired group, decision 603 examines thetone to see if the final keying sequence tone has been detected. Ifkeying sequence tone one has been detected, decision 603 will selectsubroutine check-transmit 605 which begins with decision 621. If keyingsequence tone one was not detected, the program will proceed to decision607 which examines the group tone to determine if an end-of-group tonehas been detected. If an end-of-group tone has been detected, decision607 will select item 609 which resets the group flag $00 and selects thecheck function tone subroutine 611. If an end-of-group tone has not beendetected, decision 607 will directly select the CHKFT subroutine 611.The check function tone subroutine begins with decision 613 whichexamines the detected function tone to determine if a function tonematch exists. If a function tone match has not been detected, decision613 will select the get next (GETNXT) subroutine 617 which returnsprogram control to item 565 in FIG. 25A. If a function tone match hasbeen detected, item 615 will be selected and the transmit flag will bereset to $00. Returning now to the check transmit subroutine 605,decision 621 examines the transmit flag to determine if a $FF conditionexists. If this condition does not exist, item 623 will instruct thesimulcast transmitter that a knock-down condition exists and sets the DCline disable for 90 ms. Item 625 will then set the state variable for await condition and item 627 will reset the state flag D6. State flag D6is used in the wait 3 subroutine (315A) of FIG. 27b to indicate theorigin of entry as FTX for service of PTTDLY on DC line disable. Programcontrol will then return to the background EXEC subroutine shown in FIG.19. Returning to decision 621, if a transmit flag equal to $FF conditiondoes exist, the key-up routine 629 will be selected. The Key-up 629begins with item 631 which adjusts the system state variable to indicatethe PTTDLY routine should be selected. Item 633 then clears the stateflag and returns program control to the background EXEC subroutine ofFIG. 19. Returning now to decision 597, depending on the condition ofthe group flag variable decision 597 could alternately select decision601 if the beginning of group tone (KFLAG=$00) has not been detected.Decision 601 would then check to see if the final keying sequence tonewas detected. If not, GETNXT routine 617 will be selected. If the finalkeying sequence tone one was detected, the check-transmit subroutine 605will be selected.

FIGS. 26A and 26B show a detailed flow diagram for the line PTT lockupdelay handler module 313 and 313A. This module is activated when thestate variable has been set to 4 and provides delay between the receiptof a keying sequence one tone by the simulcast paging system controldecoder in the event of unlocking line PTT. This delay is 90milliseconds and is needed to prevent the loss of line PTT during thesilent period between keying sequence tone 1 and the binary transitionsin a binary paging keying sequence. It invoked by the FTX module if thekeying sequence tone 1 is received and the transmitter is not disabled.If PTT has not been selected during a prior intervale the EXEC routinewill select PTT delay 313 since the PTT delay routine does not requirethe initialization of any variables PTT delay 313 immediately returnsprogram control to the EXEC subroutine. If PTT has been selected earlierwhen the state variable has been set to 4 the EXEC routine will selectPTT DLY3 313A which begins with item 569 which immediately sets thestate variable equal to 3 and sets the state flag. The program proceedsto item 571 which sets the timer to generate a 90 millisecond timeinterval and than subsequently returns program control to the EXECbackground subroutine shown in FIG. 19.

FIGS. 27A and 27B show detailed flow diagrams for the paging systemdecoder key-up handler routine (KEY). This module keys the simulcaststation provided the keyed A+ delay is active. Once keyed, the moduleexits to the wait state for as long as A+ delay is present. The keystate is invoked if local PTT or remote PTT or a valid keying tone isdetected by other modules. If the key module has not been previouslyinvoked the EXEC routine will select Key routine 311 since the Keyroutine does not require initialization of variables key routine 311immediately returns program control the EXEC routine. If the key routinehas been previously addressed, the EXEC routine will select the Key 3subroutine 311A which begins with item 575. Item 575 reads the value ofthe delayed keyed A+ flag P13 from port 1. Program control proceeds todecision 577 which examines the delayed keyed A+ flag. If the flag isactive, program control proceeds to the GO subroutine 581. If the flagis not active, program control proceeds to item 579 which generates a 5millisecond time delay. Program control proceeds to item 89 whichselects delayed key A+ flag. Decision 591 examines the flag if the flagis active it will pass to the GO routine 581. If the flag is still notactive, decision 591 will select item 593 which sets the state variableto 0, clears the state flag, and resets the function tone window controland the DC line disable. Item 593 then passes program control to theEXEC subroutine 303 shown in FIG. 19. Referring now to the go routine581, item 583 activates the transmitter oscillator ground by groundingoutput P16. The program then proceeds to item 585 which sets the statevariable equal to 5 to access the weight utility module. Item 587 thenresets system D6 status flag, and returns program control to thebackground EXEC routine 303.

FIGS. 28A and 28B are detailed flow diagrams of the paging systemdecoder wait de-key handler utility module. This module provides thepaging system decoder de-key function when the appropriate signal isreceived from hardware. While waiting for the de-key signal it alsounlocks the line push-to-talk after an appropriate time. This module isinvoked by a valid transmitter key-up. FIG. 28A shows the wait routinewhich is accessed by the EXEC module, if the wait routine has not beenpreviously accessed. Since this routine does not require theinitialization of variables, WAIT routine 315 returns program control tothe EXEC background routine 303. If wait has been previously addressed,the EXEC module will select WAIT 3 routine 315A as shown in FIG. 28B.Wait 3 begins with item 641 which checks the state flag variable D6 fora valid indication of a keying sequence tone. If a valid keying sequencetone has been detected decision 643 will select item 645. If the keyingsequence tone status bit D6 has not been set, program control will passto item 649 which checks port 1 pin 13 for delayed keyed A+ activity. Ifdelayed keyed A+ signal has been inactive, decision 651 passes programcontrol to items 653 and 655 which reset all outputs and returns rogramcontrol to the EXEC subroutine. If activity was detected at P13 programcontrol immediately passes from decision 651 to the EXEC subroutine 303of FIG. 19. Returning now to decision 643. If D6 flag of the status bytewas set item 645 will be selected which checks the PTT delayed timer forcurrent value. Decision 659 then passes program control to item 649 ifthe time has not elapsed, program control is passed to item 661 whichresets DC line disable outputs clears the state flag D6 and then returnsprogram control to item 649. The state flag D6 is set by the PTT delaymodule which sets the DC line disable timer that indicates to thismodule that a key up was indicated by a valid keying tone 1 tone detect.The flag is cleared after a PTT delayed time out.

In summary a paging simulcast remote control system capable ofcontrolling a paging base station in response to a predeterminedsignalling scheme has been described. Although the invention has beendescribed in terms of a preferred embodiment it will be obvious to thoseskilled in the art that many modifications and alterations may be madedeparting from the invention. Accordingly, it is intended that all suchmodifications and alterations be considered as within the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A remote control system for selective control ofparticular transmitters in a simulcast transmission system, said systemreceiving signals from a paging terminal and combining paginginformation with transmitter control information, said remote controlsystem comprising:(a) encoding means for encoding transmitter controlinformation and paging information in a predetermined sequence, whereinsaid transmitter control information comprises a series of transmitterinhibit tones; (b) linking means coupled to said encoding means fortransferring said encoded information from said encoding means; (c)individual decoding means, located at each particular transmitter,coupled to said linking means for decoding said encoded transmittercontrol information, said decoding means detecting the presence of saidseries of transmitter inhibit tones and generating a disablingtransmitter control signal in response thereto; and (d) transmittermeans coupled to said decoding means for transmitting said encodedpaging information, wherein said transmitter is further responsive tosaid disabling transmitter control signal for inhibiting thetransmission of said encoded paging information if said control signalis present.
 2. The remote control system of claim 1 wherein said encodedpaging information, and said transmitter control information aretransmitted over a common linking channel.
 3. The remote control systemof claim 1 wherein said linking means is an RF transmitter and receiver.4. The remote control system of claim 1 wherein said linking means is aconventional terrestial wire line link.
 5. The remote control system ofclaim 1 wherein said predetermined sequence comprises a transmitterinitialization tone, a series of transmitter control tones comprisingindividual transmitter control information, followed by encoded paginginformation wherein said encoded paging information includes a low levelcontrol signal which accompanies analog modulation, the absence of whichwill cause the particular transmitters to turn off so that positivestation control is maintained.
 6. The apparatus of claim 1 wherein saidencoder means further includes a plurality of switches wherein saidswitches cause said encoder to generate a signalling sequencedesignating a particular transmitter to be disabled.
 7. A method forselective control of particular transmitters in a transmission system byreceiving signals from a paging terminal and combining paginginformation with transmitter control information, said method comprisingthe steps of:(a) encoding at encoding means paging information andtransmitter control information in a predetermined sequence comprisingencoded information, said transmitter control information comprising aseries of transmitter inhibit tones; (b) transferring said encodedinformation from said encoding means to a decoding means located atparticular transmitters via linking means; (c) decoding at said decodingmeans said transmitter control information, and detecting the presenceof a particular transmitter inhibit tone corresponding to a particulartransmitter associated with said decoding means and generating adisabling transmitter control signal in response to detection thereof;and (d) transmitting paging information if said disabling transmittercontrol signal is not present or inhibiting transmission of paginginformation if said disabling transmitter control signal is present.